Heretofore centrifugal pumps have employed a spinning rotor for radially accelerating the pumped fluid. A large rotor spacing permitted maximum flow rate with minimum shear and friction losses. Impeller blades extending from the rotor surface increased the pumping drag. These prior art pumps were laminar flow devices operating at rpms below the turbulent transition speed of the carrier fluid.
Heretofore centrifugal colloid mills employed radial acceleration to force the carrier fluid through an extended shear path. The length of the gap reduced the flow rate and caused friction heating within the bulk carrier, without adding to the shear effect. The resulting higher temperature destabilized the surface complex of the colloid particles increasing the rate of readherence into agglomerates or particle clusters. Heretofore colloid mills employed static or rotating parts with corners, ridges, grooves, pins, vanes or other irregularities which produced turbulance prior to or within an extended narrow flow path thus limiting flow and increasing heating, without increasing the shear intensity. Highest shear forces for effective dispersing are not efficiently produced by promoting turbulence. In the prior art, axial input flow turns abruptly around a sharp corner through the most constricted flow area before diverging radially along the rotor. Ridges, recesses, sharp edges and rotor rotation, near the flow constriction, upset the turning flow to initiate turbulence. Once initiated, turbulence is intensified by tangential shear in the narrow flow over the spinning rotor surface. All of this turbulent fluid, enclosed between the rotor and the adjacent boundary, is pumped over the rotor perimeter. Free stream turbulence dominates flow in the region of highest shear.
The surface energy, which is related to the surface area and, the melting point of the powdered solid, must be overcome by the the shear forces to break down agglomerates to make dispersions of the ultimate particles. Some high melting point and high surface area powders, particularly carbon blacks, are quite difficult to break down into ultimate particle dispersions, especially in water.